Method and apparatus for distilling oils



Sept. 8, 1936. 'w. w. KRAFT v 2,053,670

4 METHOD AND APPARATUS FOR DISTILLING OILS Filed Feb; '14, 1935 Llam- Gnsouh:

Luamcnrms Patented Sept. 8, 1936 METHOD AND APPARATUS FOR DISTHLING OILS Wheaton .W. Kraft, East Orange, N. J., assignor to The Lummus Company, New York, N. Y., a corporation of Delaware Application February 14, 1933, Serial No. 656,677

2 Claims. (Cl. 196-94) The present invention relates to methods and apparatus for distilling oils.

One method of distilling a crude oil to divide it into a number of constituent fractions is to I heat the oil in arestricted stream and then to introduce it into a vaporizing column in which a large proportion of the components vaporize under the contained heat of the mixture. Steam may be introduced into the column to facilitate vaporization of the lighter constituents. The residue, which consists of heavy lubricating oil and/or asphaltic material, is withdrawn from the bottom of the column and the vapors pass upwardly through a series of sections of recti- 16 fying decks by which the vapors are fractionated into a number of products. One disadvantage of this method is that the large number of decks necessary for fractionation to the several products introduces a back pressure in the ,vaporiz- 20 ing zone, thereby requiring excessive temperatures or excessive quantities of steam to effect the initial vaporization of all but the heavier components of the oil.

The principal object of the present invention is to provide a method and apparatus for distilling oils in which the stripping of the residue may be eifected at minimum temperatures and without any substantial back pressure on the oils being vaporized. With this and other 36 objects in view, the present invention consists of the method and apparatus hereinafter described and particularly defined in the claims. The accompanying drawing is a diagram of the preferred apparatus for practising the prescut invention.

The crude oil, which may comprise a Pennsylvania crude, is heated in a restricted stream, as in a pipe still 2, to a temperature suflicient for vaporization of all but the heaviest lubricating 40 oils. This temperature should be below the cracking point and is preferably between 100 and 725 F. The oil thus heated is discharged into a vaporizing chamber 4 of a column 6. The vapors immediately evolved upon the release of pressure rise through the column and the residue is withdrawn from the vaporizing chamber by a pipe 8 and introduced into a stripping section l6.

The stripping section l6 may comprise a separate column I I preferably formed in the base of the column 6, being separated therefrom by an imperforate deck l2.

The vapors pass upwardly through a collecting deck l4 having an upstanding vapor pipe l6, and thence into a rectifying section l8 including 56 a number of decks for promoting contact between ascending vapors and descending liquid.

'These decks are diagrammatically illustrated in [extends upwardly from the collecting deck.

Each stripping section is provided with annular decks 34 surrounding the vapor pipe and steam 15 is introduced into the bottom of the section by a pipe 36.

The vapors, after passing the final rectifying section 24, are condensed in a condenser 38, the final condensate is decanted from the water, and 20 a part is withdrawn as a product through the valved pipe 46, the remainder passing as reflux through the pipe 42 to the top of the column. Water, which comprises the condensate of the steam introduced in the several stripping sec- 25 tions, is withdrawn at 44.

The collecting deck of each stripping section is provided with a draw-off pipe for removal of controlled stripped products rectified in the sections 24, 22, and 26, these draw-off pipes being 30 indicated at 46, 48 and 56 respectively. In addition, unstripped products may be withdrawn from intermediate decks. For example, valved draw-off pipes 52 and 54 are provided at intermediate decks of the rectifying section 24. Sim- 35 ilarly, draw-off pipes 56 and 5B are connected with the stripping section 22, and pipes 66 and 62 connected with the stripping section 26.

In the distillation of a Pennsylvania crude oil.

a gasoline of about 360 end point is withdrawn 40.

at 46, a gasoline of about 466 end point from either or both of the pipes 52 and 54, a stripped kerosene from the draw-off 46, a fuel oil from the pipe 56 or 58, a stripped gas oil from the pipe 46,

a wax distillate from the pipe 66 or 62, and a4! zation. In the section it, the oil descends over decks which are preferably of the usual boiling cap construction and steam is introduced into the bottom of the section by a pipe 66. The stripped heavy lubricating oil is withdrawn from the bottom of the section In by a pipe 68. Vapors from the section 10 are conducted by a vapor pipe 10 to'be condensed. Preferably, the condensation is eflected by passing the vapors through a surface condenser 12 maintained at a temperature to condense nearly all of the oil without any condensation of steam and bypassing the remaining vapors to a scrubber 14 where they are contacted with water admitted at 16. The purpose of the combination of the surface condenser and the scrubber is primarily to prevent condensation of steam with the oil whereby corrosive materials might be formed. As a result, the corrosive materials are localized in the scrubber I4 which may be made of such construction as to withstand corrosion. Since the oil vapors admitted to the condenser 12 are the intermediate and heavier vapors of the crude, they combine to only a small extent with steam and hence, all but a small quantity can be condensed in the surface condenser 12 without condensation of steam. The small amount of oil passing over to the scrubber I4 is too small to permit the formation of undesirable emulsions with the large volume of water present and thus a complete and effective recovery of these intermediate oils is obtained.

The ultimate material from the condenser 12 and the scrubber 14 may be obtained as a product. However, since these materials have no defln ite controlled range of boiling points, it is preferable to pass them by thepipe 18 into the column 6 above the point of the main feed. In the drawing, the pipe 18 is shown'as leading into one of the. decks of the lowermost reflux section l8.

In this section, the return liquid is contacted with the ascending hot vapors and a division of the component materials is effected. In addition to the eifect of refractionating the slop cut, the introduction of material by the pipe 18 into the section l8 performs an important function in the operation of the column as a whole. It will be understood that the removal of a number of side products from the upper portions of a column necessarily depletes the supply of reflux in the lower section. The diminution of reflux is therefore most apparent in the bottom section l8, wherein a considerable supply of reflux is necessary for the suppression of the heavy cylinder stock components, which, like the lighter components in the residue from the flashing opera tion, are present in the vapors by reason of the equilibrium existing between vapors and liquid in flash vaporization. Accordingly, the return pipe I8 is preferably introduced into the deck on which the composition of the reflux naturally existing in the column is approximately the same as that of the re-introduced slop cut. Accordingly, adequate refluxis provided for suppression of the heavy ends and, since the return of a light overhead fraction to the top of the column normally constitutes the sole source of reflux, the amount of this light material required may be very considerably reduced.

The composition of the materials withdrawn from the several draw-oils is controlled by the reflux which courses downwardly through the column. The descending liquid is ultimately collected on the deck l4, and since this material 75 has not been subjected to a stripping action, it

comprises a slop cut, which is ordinarily useful only as a cracking stock. This material may be drawn off at 64 and passed through a pipe 80 to one of the decks of the stripping section III, wherein it is subjected to the action of the steam entering through the pipe 66. As a result, any heavy residual components contained in the slop cut ultimately find their way into the residue which is withdrawn through the pipe 68 and any lighter materials are passed through the pipe- 10 to be condensed in the condenser system and returned to the column for further division. By virtue of contact with the hot vapors rising from the vaporization chamber, the condensate so re-- turned is stripped of components belonging in thenext lighter fraction, said components passing upwardly with the vapor to the column section above. The vaporization of these lighter components from the returned condensate results in a corresponding condensation from the vapors of heavier components belonging in the residue. Y

It will be seen that the residual material withdrawn at 68 is a controlled product from which substantially all components having boiling points below a predetermined value have been removed by the primary flash vaporization in the chamber 4 and by the secondary action of steam in the section ill.

The overhead product is a gasoline of controlled end point determined by the rectification in the reflux zone 24. The side products withdrawn at 46, 48 and 50 are controlled products having initial and end points determined by the action of steam in the respective stripping sections and by the controlled reflux in the rectifying sections. The materials withdrawn at the intermediate draw-offs (52, 54, 56, 58, 60 and 62) are products having boiling points intermediate to those of the stripped side products.

The material withdrawn at 64 contains some of the heavy lubricating components that come over in the flash vaporization, together with some intermediate materials, such as light lubricating oils. This is a slop cut that includes components not separated into the other more sharply defined cuts. By introducing it into the section III, it is subjected to the action of the steam and the components lighter than the desired residue are removed, while the remaining heavy components are passed into the residue. All of the components lighter than heavy lubricating oil which find their way into the section III, either through the pipe 8 or the pipe 80, are concentrated as a slop cut in the condenser system 12, 14, and by continuously returning this slop cut to the column by pipe 18 as previously described, the components constituting said cut will eventually be removed in controlled products either through the pipe 50 or the pipe 68.

In the usual process, the initial vaporization with steam occurs in the main column. According to the present invention, the initial vaporization, without steam, in the chamber 4 effects removal of the greater part of the intermediate and light oils, and the remainder of said oils is removed in the section l0. It is the vaporization of the last remnants of the intermediate and light oils that usually offers the greatest difliculty, and frequently requires either excessive heating or inordinately large quantities of steam. Although the overhead condenser may be at atmospheric pressure, the vaporizing zone may be at a pressure several pounds above atmosphere,

due to the back pressure introduced by the decks 75 out condensing the steam, condensing the rein the rectifying zones. .In the present invention, the steam stripping section II! is under aconsiderably reduced pressure, as compared with the pressure in the main column, and the removal of the final remnants of the intermediate and light oils can be effected with a saving of steam, and without the necessity of initially heating to an unsafe temperature.

Having thus described the invention, what is claimed is: v

1. The method of distilling oils which consists in heating the oil in a restricted stream, introducing the heated oil into a vaporizing zone to evolve vapors by flash vaporization, passing the vapors from the vaporizing zone through a rectifying zone, contacting the vapors with descending liquid in the rectifying zone, collecting and withdrawing reflux liquid at the bottom of the rectifying zone while preventing passage of reflux into the vaporizing zone, passing the residue of the vaporizing operation and the withdrawn reflux to a stripping zone unconnected with the vaporizing zone, introducing steam into the stripping zone, condensing the oil vapors from the stripping section by surface condensation withmainder of the steam-oil mixture by direct contact with water in suflicient quantity to prevent formation of emulsions, and passing oil condensate to the rectifying zone.

2. Apparatus for distilling crude oil comprising a heater, a columnhaving a flash vaporizing chamber, a rectifying section abovethe vaporizing chamber, means for passing reflux liquid downwardly through the rectifying section, a

stripping section unconnected with the column, means for passing residue from the column to the stripping section, means for introducing steam into the stripping section, a collecting deck immediately above the vaporizing chamber to collect reflux liquid as a slop cut and constructed to prevent passage of liquid into the vaporizing zone, means for passing the slop cut to the stripping section, a surface condenser for condensing the oils from the stripping section without condensation of steam, a scrubber for condensing the steam and any remnant of oil therewith, and means for passing oil from the condenser and scrubber to one of the rectifying sections.

WHEATON W. KRAFT. 

